Method of manufacturing self-aligned interconnects by deposition of a non-conformal air-gap forming layer having an undulated upper surface

ABSTRACT

A method of forming an interconnect to an electrical device is provided. The structure produced by the method may include a plurality of metal lines in a region of a substrate positioned in an array of metal lines all having parallel lengths; and a plurality of air gaps between the metal lines in a same level as the metal lines, wherein an air gap is present between each set of adjacent metal lines. A plurality of interconnects may be present in electrical communication with said plurality of metal lines, wherein an exclusion zone for said plurality of interconnects is not present in said array of metal lines.

BACKGROUND Technical Field

The present invention relates to electrical devices, and moreparticularly, to interconnect structures in electrical devices.

Description of the Related Art

Back end of the line (BEOL) resistance and capacitance are importantparameters in interconnect performance, typically documented as RCproduct. As the dimensions of electrical devices, such as semiconductorand memory devices, continue to scale, i.e., be reduced, the resistancetypically increases exponentially, while the capacitance increaseslinearly (or remains constant through material changes). The interest inreducing the RC product has driven reducing the capacitance by reducingthe dielectric constant of some of the dielectric materials being usedin electrical devices.

SUMMARY

The present disclosure is directed to interconnects in electricaldevices including air gap structures, and methods of forminginterconnects to electrical devices including air gap structures. In oneembodiment, the method may include forming a plurality of metal lines.At least one air gap is formed between adjacent metal lines in saidplurality of metal lines by depositing a non-conformal material stackatop the plurality of metal lines, the material stack includes an airgap forming dielectric and a hard mask dielectric layer. A firstinterlevel dielectric layer is formed atop the material stack, wherein atrench is present in the interlevel dielectric exposing an apex of thenon-conformal material stack substantially aligned to a metal line ofthe plurality of metal lines. An exposed portion of an apex portion ofthe hard mask dielectric layer is removed selectively to the air gapforming dielectric. A second trench is formed through the air gapforming dielectric using a remaining portion the hard mask dielectriclayer as an etch mask to expose a metal line without opening said atleast one air gap. A contact to the air gap is formed in at least thesecond trench.

In another embodiment, a method of forming an interconnect to anelectrical device is provided that includes forming at least one air gapbetween adjacent metal lines in a plurality of metal lines, and forminga sacrificial filler material within the at least one air gap. Apermeable cap dielectric is formed atop the sacrificial filler material.A contact is formed to a metal line of the plurality of metal lines. Atleast one of the permeable cap dielectric and the sacrificial fillermaterial obstruct the contact from filling said at least one air gap.The sacrificial filler material is removed.

In another aspect of the present disclosure, an electrical device isprovided that includes a plurality of metal lines in a region of asubstrate positioned in an array of metal lines all having parallellengths, and a plurality of air gaps between the metal lines in a samelevel as the metal lines. The air gaps are present between each set ofadjacent metal lines. A plurality of interconnects are in electricalcommunication with the plurality of metal lines. An exclusion zone forsaid plurality of interconnects is not present in the array of metallines.

In yet another aspect of the present disclosure, an electrical device isprovided that includes a plurality of metal lines in a region of asubstrate positioned in an array of metal lines all having parallellengths; and a plurality of air gaps between the metal lines in a samelevel as the metal lines, wherein an air gap is present between each setof adjacent metal lines. The electrical device may further include aplurality of interconnects in electrical communication with saidplurality of metal lines, in which the plurality of interconnectsincludes interconnects that are present extending over an air gap, butdo not extend into the air gap. In some examples, the bottom surface ofthe interconnect provides a portion of an upper surface of the air gap.In some examples, a permeable dielectric cap is adjacent to the bottomsurface of the interconnect and provides an abutting upper surface ofthe air gap adjacent to the upper surface of the air gap provided by theinterconnect.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a side cross-sectional view depicting one embodiment of aplurality of metal lines, and forming a metal cap layer on an uppersurface of the plurality of metal lines, in accordance with oneembodiment of the present disclosure.

FIG. 2 is a side cross-sectional view depicting damaging a portion of alow-k dielectric material that is separating adjacent metal lines, inaccordance with one embodiment of the present disclosure.

FIG. 3 is a side cross-sectional view depicting removing the damagedportion of the low-k dielectric and forming a conformal dielectric layeron sidewalls and upper surfaces of said plurality of metal lines, inaccordance with one embodiment of the present disclosure.

FIG. 4 is a side cross-sectional view depicting one embodiment offorming at least one air gap between adjacent metal lines in theplurality of metal lines by depositing a non-conformal material stackatop the plurality of metal lines, wherein the material stack includesan air gap forming dielectric and a hard mask dielectric layer, inaccordance with the present disclosure.

FIG. 5 is a side cross-sectional view depicting one embodiment offorming a first etch mask over a bilayer of a metal nitride layer and anitride containing dielectric that provides the hard mask dielectriclayer, wherein an opening in the etch mask is overlying at least one ofsaid metal lines and at least one of said air gaps, and removing anexposed portion of the metal nitride layer in said opening selectivelyto the nitride containing dielectric of the bilayer, in accordance withthe present disclosure.

FIG. 6 is a side cross-sectional view depicting one embodiment offorming an interlevel dielectric layer atop the material stack, whereinan opening is present in the interlevel dielectric exposing an apex ofthe non-conformal material stack substantially aligned to a metal lineof the plurality of metal lines, and removing an exposed portion of anapex portion of the hard mask dielectric layer selectively to the airgap forming dielectric, in accordance with the present disclosure.

FIG. 7 is a side cross-sectional view depicting one embodiment offorming a trench through the air gap forming dielectric using aremaining portion the hard mask dielectric layer as an etch mask toexpose a metal line without opening said at least one air gap, inaccordance with the present disclosure.

FIG. 8 is a side cross-sectional view depicting filling the trencheswith a plug material prior to forming the contact to the metal line.

FIG. 9 is a side cross-sectional view depicting recessing the plugmaterial to expose the remaining portion of the hard mask for removal byetching, in accordance with one embodiment of the present disclosure.

FIG. 10 is a side cross-sectional view depicting forming a contact tothe metal lines, in accordance with one embodiment of the presentdisclosure.

FIG. 11 is a side cross-sectional view depicting forming at least oneair gap between adjacent metal lines in a plurality of metal lines, inaccordance with one embodiment of the present disclosure.

FIG. 12 is a side cross-sectional view depicting forming a sacrificialfiller material within the at least one air gap, and forming a permeablecap dielectric atop the sacrificial filler material, in accordance withone embodiment of the present disclosure.

FIG. 13 is a side cross-sectional view depicting forming a trench for acontact on the structure depicted in FIG. 12.

FIG. 14 is a side cross-sectional view depicting forming a contact to ametal line of the plurality of metal lines, and removing saidsacrificial filler material, in accordance with one embodiment of thepresent disclosure.

FIG. 15 is a top down view depicting an interconnect structure to metallines separated by air gaps that does not include an exclusion zone, inaccordance with one embodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments is intended to be illustrative,and not restrictive. Further, the figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure. Forpurposes of the description hereinafter, the terms “upper”, “lower”,“right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, andderivatives thereof shall relate to the embodiments of the disclosure,as it is oriented in the drawing figures. The terms “positioned on”means that a first element, such as a first structure, is present on asecond element, such as a second structure, wherein interveningelements, such as an interface structure, e.g. interface layer, may bepresent between the first element and the second element. The term“direct contact” means that a first element, such as a first structure,and a second element, such as a second structure, are connected withoutany intermediary conducting, insulating or semiconductor layers at theinterface of the two elements.

In some embodiments, the methods and structures disclosed herein providea structure and method for maximizing air gap usage in back end of theline interconnects through via landing modification. Metal vias may alsobe referred to as contacts throughout the present disclosure.

BEOL resistance and capacitance are the critical parameters ininterconnect performance, typically documented as the RC product. Theneed to minimize the RC product has driven the reduction in thecapacitance through lowering of the dielectric constant. One solutionfor reducing the dielectric constant is the incorporation of air gapsbetween interconnects (k=1). Typically, air gap structures are carefullyplaced within circuits to prevent via structures from landing thereon,i.e., possibly from above, and entering an air gapped region, which canresult in producing electrical shorts. This can lead to a reduction intotal amount of air gaps that can be positioned within an electricaldevice, in which exclusion zones are positioned around areas in whichvias are to land, reducing the effectiveness of the air gap structure.In some embodiments, the methods and structures disclosed herein createa fully aligned via compatible with maximized air gap utilization. Insome embodiments, the methods and structures disclosed herein fill airgaps with a sacrificial material to prevent via landing shorts. In someembodiments, the methods and structures disclosed herein providemultilevel air gap structures, wherein the upper level via is fullyaligned with and/or captured on an underlying barrier dielectric surfaceoverlying the lower interconnect level, such that bridging of themisaligned upper level via to an air gap in the lower interconnect levelis avoided. The methods and structures disclosed herein avoidinterconnect to air gap misalignment without the use of restrictive vialanding design rules that can restrict the location and area of theallowable air gap regions. The methods and structures of the presentdisclosure are now discussed with more detail referring to FIGS. 1-15.

FIGS. 1-10 depict one embodiment of a method for forming self-alignedand fully landed vias in a multi-level air gap interconnect structureleveraging the inherent topography of the air gap forming chemical vapordeposition (CVD) deposited dielectric, i.e., air gap forming dielectric25. As will be further described below, the method includes the steps ofdepositing a non-conformal second level CVD dielectric, e.g., air gapforming dielectric 25, over an etched back first level interconnect,i.e., low-k dielectric layer 5 after the first level dielectric isremoved from between the metal lines, such that pinched off air gaps 20are formed in the first level with an overlying undulating surfacetopography in the second dielectric, e.g., air gap forming dielectric25. This topography has high points, i.e., apexes, at locations abovethe first level interconnect lines, i.e., metal lines 20, and low pointsat the locations where air gaps 20 are located. In some embodiments, atwo layer hard mask stack 30, 35 is formed on it, an organic planarizinglayer (OPL) 51 is applied to fill the topography atop the hard maskstack 30, 35. A line level litho and etch is performed first to open atrench pattern in the top hard mask layer, then the organic planarizinglayer (OPL) 51, and a via lithography process is done to form oversizedvia openings to a controlled depth in the organic planarizing layer(OPL) 51 such that the hard mask stack 30, 35 is only etched at the highpoints of the topography above the interconnect lines 10 (also referredto as metal lines 10) in the first level. The sec air gap formingdielectric 25 is etched to form the vias which are self-aligned and landatop the lower level interconnect lines only, i.e., metal lines 10 only.As the high points always exclude the location of the air gaps 20 in thelevel below, the method yields via landing that automatically excludesthe underlying air gap locations.

FIG. 1 depicts one embodiment of a plurality of metal lines 10, andforming a metal cap layer 12 on an upper surface of the plurality ofmetal lines 10. The metal lines 10 may be arranged in an arrayconfiguration, in which the length of the adjacent metal lines 10 runssubstantially parallel to one another. The metal lines 10 can provideelectrical communication horizontally across an electrical device fromone region of the electrical device to another, and can also be incommunication with vias that bring the electrical signals to theinterconnects and related structures across the electrical device.

The metal lines 10 may be composed of any electrically conductivematerial. For example, the metal lines 10 may be composed of copper,silver, platinum, aluminum, gold, tungsten and combinations thereof. Inother embodiments, the metal lines 10 may be composed of an n-typesemiconductor material, such as n-type polysilicon. The metal lines 10may have a height H1 ranging from 20 nm to 1000 nm, and a width W1ranging from 5 nm to 500 nm. In another embodiment, the metal lines 10may have a height H1 ranging from 20 nm to 100 nm, and a width W1ranging from 10 nm to 80 nm. The pitch P1 separating the adjacent metallines may range from 20 nm to 1000 nm. In another embodiment, the pitchP1 may range from 30 nm to 80 nm. In yet another embodiment, the pitchP1 may range from 40 nm to 50 nm.

The metal lines 10 may be formed in trenches that are forming in a low-kdielectric layer 5 that is overlying a substrate (not shown). Thesubstrate may include a semiconductor wafer, such as a type IVsemiconductor wafer, e.g., silicon wafer, or a type III-V semiconductorwafer, such as a compound semiconductor, e.g., gallium arsenidesemiconductor wafer. In one embodiment, a number of dielectric layersand semiconductor material layers can be arranged with the substrate toprovide microelectronic devices, or smaller devices, which can includesemiconductor devices, such as field effect transistors (FETs), fin typefield effect transistors (FinFETs), bipolar junction transistors (BJT)and combinations thereof. The at least one device layer may also includememory devices, such as dynamic random access memory (DRAM), embeddeddynamic random access memory (EDRAM), flash memory and combinationsthereof. The at least one device layer can also include passive devices,such as resistors and capacitors, as well as electrical connections tothe devices containing within the at least one device layer.

The low-k dielectric layer 5 can be present atop the above describedsubstrate. The term “low-k” denotes a material having a dielectricconstant that is less than the dielectric constant of silicon dioxide(SiO2). For example, a low-k dielectric material for the intraleveldielectric layer 10 may have a dielectric constant that is less than4.0, e.g., 3.9. In one embodiment, the low-k dielectric material mayhave a dielectric constant ranging from 1.75 to 3.5. In anotherembodiment, the low-k dielectric layer 5 may have a dielectric constantranging from 2.0 to 3.2. In yet an even further embodiment, the low-kdielectric layer 5 may have a dielectric constant ranging from 2.25 to3.0. Examples of materials suitable for the low-k dielectric layer 5 mayinclude organosilicate glass (OSG), fluorine doped silicon dioxide,carbon doped silicon dioxide, porous silicon dioxide, porous carbondoped silicon dioxide, spin-on organic polymeric dielectrics (e.g.,SILK™), spin-on silicone based polymeric dielectric (e.g., hydrogensilsesquioxane (HSQ) and methylsilsesquioxane (MSQ), and combinationsthereof.

In some embodiments, the plurality of metal lines 10 may be formed inthe low-k dielectric layer 5 by a process sequence that includes forminga plurality of line trenches in a low-k dielectric layer, forming aliner material 11 in the line trenches, and forming the plurality ofmetal lines 10 on the liner material 11 in the line trenches. The linetrenches may be formed by forming a photoresist mask on the uppersurface of the low-k dielectric layer 5, and etching the low-kdielectric layer 5 using an etch process, such as reactive ion etch. Theliner material 11 is typically a conformal layer, and is typicallyformed on the sidewalls and base of the line trenches. The term“conformal” denotes a layer having a thickness that does not deviatefrom greater than or less than 30% of an average value for the thicknessof the layer. The liner material 11 may be a seed layer for forming thematerial for the metal lines 10. Examples of compositions for the seedlayer may be metals, such as copper or aluminum. The liner material 11may also be a diffusion barrier, such as a metal nitride, e.g., tantalumnitride, tungsten or titanium nitride. The liner material 11 may beformed using chemical vapor deposition (CVD), atomic layer deposition(ALD), or physical vapor deposition (PVD), and can have a thicknessranging from 1 nm to 10 nm, and in some examples having a thicknessranging from 2 nm to 5 nm. Examples of CVD suitable for forming theliner material 11 include plasma enhanced CVD (PECVD). Examples of PVDsuitable for forming the liner material 11 include plating,electroplating, electroless plating, sputtering and combinationsthereof. The metal lines 10 may be deposited to fill the line trenches.The metal lines may be formed using chemical vapor deposition (CVD),e.g., plasma enhanced CVD (PECVD); atomic layer deposition (ALD), orphysical vapor deposition (PVD), e.g., plating, electroplating,electroless plating, sputtering and combinations thereof. Aplanarization process may be applied to the upper surface of thedeposited material for the metal lines, so that the upper surfaces ofthe metal lines are coplanar with the upper surface of the low-kdielectric layer 5.

FIG. 1 also depicts selectively forming a metal cap layer 12 on an uppersurface of the plurality of metal lines 10. By selectively formed it ismeant that the deposition process for forming the metal cap layer 12deposits the metal material for the metal cap layer 12 only on the uppersurface of the metal lines 10 without forming the metal material on theupper surface of the low-k dielectric material 5. The metal cap layer 12may be composed of cobalt (Co), tungsten (W) and ruthenium (Ru). Themetal cap layer 12 may have a thickness ranging from 1 nm to 10 nm, andin some examples may range from 2 nm to 5 nm. The metal cap layer 12 maybe deposited using a chemical vapor deposition (CVD) apparatus or anatomic layer deposition (ALD) apparatus. Further details regarding theselective forming for the material of the metal cap layer 12 may befound in U.S. Pat. Nos. 4,517,225, 4,853,347 and U.S. Patent ApplicationPublication No. 2009/0269507, which are incorporated herein byreference.

FIG. 2 depicts damaging a portion of a low-k dielectric material 5 thatis separating adjacent metal lines 10. The damage step may be providedby a plasma operation that removes the carbon from the low-K dielectriclayer 5. The plasma may include an oxygen plasma, an ammonia plasma,nitrogen or hydrogen plasma. The plasma process is continued until athickness of the low-k dielectric layer 5 extending substantially to thebase of the metal lines 10 is damaged (identified by damaged portion 5a).

FIG. 3 depicts one embodiment of removing the damaged portion 5 a of thelow-k dielectric 5, and forming a conformal dielectric layer 15 onsidewalls and upper surfaces of said plurality of metal lines 10. Thedamaged portion 5 a of the low-k dielectric 5 can be removed by an etchprocess that is selective to the portion of the low-k dielectric 5 thathas not been damaged. As used herein, the term “selective” in referenceto a material removal process denotes that the rate of material removalfor a first material is greater than the rate of removal for at leastanother material of the structure to which the material removal processis being applied. For example, in one embodiment, a selective etch mayinclude an etch chemistry that removes a first material selectively to asecond material by a ratio of 100:1 or greater. The etch process forremoving the damaged portion 5 a of the low-k dielectric 5 may also beselective to the metal cap layer 12. In some embodiments, the damagedportion 5 a of the low-k dielectric 5 may be removed using a wet or dryetch process. In one embodiment, the damaged portion 5 a of the low-kdielectric 5 is removed by reactive ion etch (RIE). Removing the damagedportion 5 a of the low-k dielectric 5 forms a space between adjacentmetal lines.

The conformal dielectric layer 15 may be a continuous layer that extendsacross the entire substrate, and is present on the sidewall surfaces andupper surface of the metal lines 10, as well as the portion of the low-kdielectric 5 present in the space between the metal lines 10 on thelow-k dielectric 5. The conformal dielectric layer 15 may be composed ofan oxide, nitride, or oxynitride material. For example, when theconformal dielectric layer 15 is composed of a nitride, the conformaldielectric layer 15 may be silicon nitride. The conformal dielectriclayer 15 may have a thickness ranging from 1 nm to 10 nm. In someembodiments, the conformal dielectric layer 15 has a thickness rangingfrom 2 nm to 5 nm. The conformal dielectric layer 15 may be formed usingchemical vapor deposition, such as plasma enhanced CVD (PECVD), oratomic layer deposition (ALD).

FIG. 4 depicts one embodiment of forming at least one air gap 20 betweenadjacent metal lines 10 in the plurality of metal lines by depositing anon-conformal material stack 25, 30, 35 atop the plurality of metallines 10. In some embodiments, the material stack includes an air gapforming dielectric 25 and a hard mask dielectric layer 30, 35. The airgap forming dielectric 25 is typically non-conformally deposited andencloses the air gaps 20 within said space between said adjacent lines10 by pinching off the opening to the space. The air gap formingdielectric 25 is typically composed of a low-k dielectric. Examples ofmaterials suitable for the low-k dielectric material that provides airgap forming dielectric 25 may include silicon carbon boron nitride(SiCBN), silicon oxycarbonitride (SiOCN), fluorine doped silicondioxide, carbon doped silicon dioxide, porous silicon dioxide, porouscarbon doped silicon dioxide, organosilicate glass (OSG), diamond-likecarbon (DLC) and combinations thereof.

The air gap forming dielectric 25 is deposited using process that canprovide a poor step coverage that can produce the undulating uppersurface that is depicted in FIG. 4. The undulating upper surface ischaracterized by alternative apexes and recesses in a wave likegeometry. The apexes of the upper surface of the air gap formingdielectric 25 are aligned, i.e., self-aligned, to be centered over themetal lines 10, and the recessed portion of the upper surface of the airgap forming dielectric 25 are aligned to the air gaps 20. The thicknessof the air gap forming dielectric 25 can be selected to ensureencapsulation of the air gaps 20. The air gaps 20 typically have a widthW2 ranging from 10 nm to 500 nm.

Referring to FIG. 4, in some embodiments, the hard mask dielectric layeris composed of a bilayer of a nitride containing dielectric 35 presenton the low-k dielectric air gap forming dielectric 25, and a metalnitride 30 that is present atop the nitride containing dielectric 35. Insome embodiments, the material layers that provide the hard maskdielectric are conformally formed layers, which are formed entirety atopthe undulating surface of the air gap forming dielectric 25. Forexample, the nitride containing dielectric 35 may be silicon nitride,and have a thickness ranging from 1 nm to 10 nm. In some embodiments,the nitride containing dielectric 35 has a thickness ranging from 2 nmto 5 nm. The nitride containing dielectric 35 may be formed usingchemical vapor deposition, such as plasma enhanced CVD (PECVD), oratomic layer deposition (ALD).

The metal nitride layer 30 can be a conformally formed layer. The metalnitride layer 30 may be composed of a metal nitride that is selectedfrom the group consisting of titanium nitride, tantalum nitride,tungsten nitride and a combination thereof. The metal nitride layer 30may have a thickness ranging from 1 nm to 10 nm. In another embodiment,the metal nitride layer 30 may have a thickness ranging from 2 nm to 5nm. The metal nitride layer 30 may be formed using chemical vapordeposition (CVD), such as plasma enhanced CVD (PECVD); atomic layerdeposition (ALD); or physical vapor deposition (CVD), such as sputteringand plating.

FIG. 5 depicts one embodiment of forming a first etch mask 40 over abilayer of the metal nitride layer 30 and the nitride containingdielectric layer 35 that provides the hard mask dielectric layer,wherein an opening 45 in the etch mask 40 is overlying at least one ofsaid metal lines and at least one of said air gaps. Forming the etchmask 40 may begin with forming an organic planarization layer (OPL) 41.The organic planarization layer (OPL) 41 may be an organic polymer, suchas polyacrylate resin, epoxy resin, phenol resin, polyamide resin,polyimide resin, unsaturated polyester resin, polyphenylenether resin,polyphenylenesulfide resin, or benzocyclobutene (BCB). The opening 45may be formed through the OPL layer using photolithography and etchprocesses. For example, an antireflective coating 42, e.g., SiARC, maybe formed atop the OPL layer 41, followed by a photoresists mask 43. Forexample, a photoresist mask 43 may be formed overlying the OPL layer 41using deposition and photolithography, in which the openings in thephotoresist mask correspond to the portions of the OPL layer 41 that areetched to provide the opening 45. More specifically, in one embodiment,a photoresist pattern (also referred to as photoresist mask) is producedby applying a photoresist to the surface to be etched; exposing thephotoresist to a pattern of radiation; and then developing the patterninto the photoresist utilizing a resist developer. Once the patterningof the photoresist is completed, the sections covered by the photoresistare protected while the exposed regions are removed using a selectiveetching process that removes the unprotected regions. The exposedportions of OPL layer 41 may then be etched to provide the opening 45using the photoresist mask 43 as an etch mask. The etch process forforming the opening 45 may include an anisotropic etch, such as reactiveion etch, laser etching, plasma etching, or a combination thereof.

FIG. 5 depicts one embodiment of removing an exposed portion of themetal nitride layer 30 exposed by the opening 45 selectively to thenitride containing dielectric 35 of the bilayer that provides the hardmask. The etch process for removing the exposed portion of the metalnitride layer 30 may be selective to the nitride containing dielectric34 and the OPL layer 41. The etch process for removing the exposedportion of the metal nitride layer 30 may be a wet etch process, or adry etch, e.g., gas plasma etching or reactive ion etch.

Following removal of the exposed portion of the metal nitride layer 30,the OPL layer 41, the SiARC layer 42 and the photoresist mask 43 may bestripped from the structure depicted in FIG. 5. In some embodiments, themetal nitride layer 30, the OPL layer 41, the SiARC layer 42 and thephotoresist mask 43 are removed using a selective etch, such as a wetchemical etch.

FIG. 6 depicts one embodiment of forming a layered stack including asacrificial dielectric layer 51 atop the material stack 30, 35, whereinan opening 55 is present in the sacrificial dielectric 51 exposing anapex A1 of the non-conformal material stack substantially aligned to ametal line 10 of the plurality of metal lines. The sacrificialdielectric layer 51 may be composed of an organic planarization layer(OPL) 51 that is similar to the organic planarization layer 41 describedabove with reference to FIG. 5. Therefore, in some embodiments, theabove description of the organic planarization layer 41 depicted in FIG.4 may provide an example for one embodiment of a sacrificial dielectriclayer 51, as depicted in FIG. 5. The opening 55 is formed in thesacrificial dielectric layer 51 using deposition, photolithography andetch processes. For example, a photoresist etch mask 53 andantireflective coating 52 may be used in combination with an etchprocess, such as reactive ion etch, may be used to form the opening 55.The width of the opening 55 exposes the nitride containing dielectriclayer 35 that is present on the apex A1 of the undulating upper surfaceof the air gap forming dielectric 25 that is aligned with the underlyingmetal line 20, while a remaining portion of the nitride containingdielectric layer 35 is covered by a remaining portion of the sacrificialdielectric layer 51.

The depth of the opening 55 is selected so that the opening only exposesthe nitride containing dielectric layer 35 that is present on the apexA1 of the undulating surface of the air gap forming dielectric 25, butthe depth of the opening 55 does not extend to expose the portions ofthe nitride containing dielectric layer 35 that is present on therecessed portions of the undulating surface of the air gap formingdielectric 25. The etch process for forming the opening 55 may be ananisotropic etch. As used herein, the term “anisotropic etch process”denotes a material removal process in which the etch rate in thedirection normal to the surface to be etched is greater than in thedirection parallel to the surface to be etched. The anisotropic etchprocess that provides the opening 55 may be a reactive ion etch (RIE)process. Other examples of anisotropic etching that can be used at thispoint of the present disclosure include ion beam etching, plasma etchingor laser ablation. To determine the depth of the opening 55 that exposesonly the apex portions of the nitride containing dielectric layer 35,the etch process for forming the opening 55 may be timed. In otherembodiments, end point detection methods may be used to terminate theetch process for forming the opening 55.

FIG. 6 depicts one embodiment of removing an exposed portion of an apexportion of the hard mask dielectric layer, i.e., the apex portion of thenitride containing dielectric layer 35, selectively to the air gapforming dielectric 25 and the sacrificial dielectric layer 51. The etchprocess for removing the exposed portions of the nitride containingdielectric layer 35 that is present on the apex portion of the air gapforming dielectric 25 may be a wet etch process or a dry etch process.Examples of dry etch processes suitable for being employed at this stageof the present disclosure may include reaction ion etching or gas plasmaetching.

FIG. 7 depicts one embodiment of forming a trench 60 through the air gapforming dielectric 25 using a remaining portion the photoresist mask 53and the patterned portion, i.e., opening 55, of the sacrificialdielectric layer 51 as an etch mask to expose a metal line 10. Becausethe trench 60 is formed using an anisotropic etch that removes theexposed air gap forming dielectric 25, and the exposed air gap formingdielectric 25 is aligned to an underlying metal line 10, the trench 60is aligned to the underlying metal line 10. The exposed air gap formingdielectric 25 is aligned to the underlying metal line 10, because theexposed air gap forming dielectric 25 is the apex portion of theundulating upper surface of the air gap forming dielectric, which isaligned to the metal lines 10. The etch process for forming the trench60 may also be selective to the metal cap layer 12 atop the metal lines10. The etch process for forming the trench 60 may be provided byreactive ion etch (RIE). Other examples of anisotropic etching that canbe used at this point of the present disclosure include ion beametching, plasma etching or laser ablation.

FIG. 8 depicts filling the trenches 60 with a plug material 65 prior toforming the contact to the metal line. Before filling the trenches, thephotoresist mask 53, antireflective coating 52 and the sacrificialdielectric layer 51 may be removed. Thereafter, the exposed portion ofthe nitride containing dielectric layer 35 may be remove by an etch thatis selective to the remaining portion of the metal nitride layer 30 andthe sacrificial dielectric layer 51. The trench 60 may then be filledwith a via plug material, such as SiARC or organo-siloxane (RxCH3ySiOz)polymer (R=organic chromophore) marketed under the tradename DUO fromHoneywell. In other examples, the via plug material may be composed oforganic dielectric materials that can be employed in the inventioninclude, but are not limited to: diamond-like carbon (DLC), fluorinatedDLC, polyimides, fluorinated polyimides, parylene-N, parylene-F,benzocyclobutanes, poly(arylene ethers), polytetrafluoroethylene (PTFE)derivatives marketed by Du Pont de Nemours, Inc. under the registeredtrademark Teflon AF, poly(naphthalenes), poly(norbornenes), foams ofpolyimides, organic xerogels, porous PTFE and other nano-, micro- ormacro-porous organic materials. The plug material 65 may be depositedusing chemical vapor deposition, solution deposition or spin ondeposition. Following deposition, the plug material 65 may beplanarized, e.g., by chemical mechanical planarization (CMP), to providethe structure depicted in FIG. 8.

FIG. 9 depicts one embodiment of recessing the plug material 65 toexpose the remaining portion of the hard mask 30, 35 for removal byetching. The plug material 65 may be recessed by an etch that includeswet chemical etching or reactive ion etching. The remaining portion ofthe hard mask 30, 35 may be removed by an etch process that is selectiveto the air gap forming dielectric 25.

FIG. 10 depicts forming a contact 75 to the metal lines 10. Forming thecontact 75 may include forming a contact liner 73 followed by anelectrically conductive fill material 74. The contact liner 73 may be aseed layer, diffusion barrier or adhesion layer that can be depositedusing at least one of atomic layer deposition (ALD), chemical vapordeposition (CVD), plasma vapor deposition (PVD), pulsed nucleation layer(PNL), pulsed deposition layer (PDL), plasma-enhanced ALD andplasma-enhanced CVD. The contact liner 73 may be composed of a metal,such as copper, aluminum, tungsten, tantalum, titanium and combinationsthereof. The electrically conductive fill material 74 may be formedusing a deposition method, such as CVD or PVD. Examples of PVD methodssuitable for forming the electrically conductive fill material 74include sputtering, plating, electroplating, electroless plating, andcombinations thereof. The electrically conductive fill material 74 mayinclude, but is not limited to: tungsten, copper, aluminum, silver, goldand alloys thereof. Following deposition, the upper surface of theelectrically conductive fill material may be planarized, e.g.,planarized by chemical mechanical planarization (CMP), to produce thestructure depicted in FIG. 10, in which the trench portion of thecontact 75 is self-aligned to the metal line 10, and does not open theair gaps 20.

In a second embodiment, a sacrificial filler 85 is used between a lowerinterconnect conductor lines 10 after a dielectric etch back step and apermeable cap 66 is formed atop the interconnect structure. The nextlevel interconnect is formed with vias 90 connecting to the lowerinterconnect level, wherein any misaligned portion of the vias isprevented from punching through by the permeable cap 86 and/or theunderlying sacrificial fill material 85. The sacrificial fill material85 is then removed through the permeable cap layer 86 to form an air gap20 in the lower interconnect level. In this embodiment, any misalignedvias 90 in this structure are landed on the permeable hard mask 86, andhence does not punch through into the lower interconnect level or airgaps 20. Further details of this method are now described with referenceto FIGS. 11-14.

FIG. 11 depicts forming at least one air gap 20 between adjacent metallines 10 in a plurality of metal lines 10. The metal lines 10 depictedin FIG. 11 are similar to the metal lines 10 that are described abovewith reference to FIG. 1. Therefore, the description of the metal lines10, e.g., their composition and method of forming, that has beenprovided above referencing the structures depicted in FIG. 1, issuitable for one embodiment of a metal line 10 as depicted in FIG. 11.For example, the metal lines 10 that are depicted in FIG. 11 may includea diffusion barrier liner 11 a, a seed layer 11 b, and an electricallyconductive portion that provide the metal line. The metal lines 10 maybe formed using a method that includes forming a plurality of linetrenches in a low-k dielectric layer 5, forming a liner material 11 a,11 b in the line trenches; and forming the plurality of metal lines 10on the liner material 11 a, 11 b in the line trenches. The low-kdielectric material 5 that is depicted in FIG. 11 can be provided by thelow-k dielectric layer 5 that is described above with reference toFIG. 1. The low-k dielectric material 5 may be present atop a substrate1. Examples of substrates suitable for the embodiment described withreference to FIGS. 11-14 is also provided in the above description ofFIG. 1.

The air gaps 20 may be formed in the low-k dielectric layer 5 betweenthe adjacent metal lines 10 using an etch process, such as a wetchemical etch, or a dry etch, such as reactive ion etch or gas phaseetching.

FIG. 12 depicts forming a sacrificial filler material 85 within the atleast one air gaps 20, and forming a permeable cap dielectric 86 atopthe sacrificial filler material 85. The sacrificial filler material 85may be, but need not be, a dielectric. In some embodiments, thesacrificial filler material 85 will cleanly decompose within a time andtemperature range, and in an atmosphere, which will not adversely affectthe function of other structural components. In some embodiments, anacceptable decomposition temperature would be at or about 350° C.-450°C. Examples of suitable materials to function as a sacrificial layerinclude: polystyrenes; polymethyl methacrylates; polynorbornenes; andpolypropylene glycols. Cross linking of the organics by UV or electronbeam exposure has the benefit of rendering those temporary dielectriclayers insoluble to organic solvents used during processing.

The sacrificial filler material 85 may be deposited using chemical vapordeposition (CVD), chemical solution deposition, and/or spin ondeposition. The time period for depositing the sacrificial fillermaterial 85 is selected to fill the air gaps 20. A planarization processmay be applied to the upper surface of the sacrificial filler material85 following deposition, such as chemical mechanical planarization, sothat an upper surface of the sacrificial filler material 85 is coplanarwith an upper surface of the low-k dielectric layer 5 and the metallines 10, as depicted in FIG. 12.

FIG. 12 also depicts forming a permeable cap dielectric 86 atop thesacrificial filler material 85. The term “permeable” denotes that asolid material allows for the decomposing sacrificial filler material 85to outgas through the permeable solid material. In some embodiments, thepermeable cap dielectric 86 that is formed atop the sacrificial fillermaterial 85 comprises crosslinked polyphenylenes, porous SiCOH, SiCOH,methyl silsesquioxane (MSSQ), crosslinked polyphenylenes orcombinations. Examples of suitable materials to function as a permeablecap dielectric 86 include: HoSP and HoSP Best, products of HoneywellElectronic Materials; JSR 5140, JSR 2021, products of JSR Micro; SiCOH,polycarbonate or combinations of any of these materials, optionallyarranged as a bi-layer. The permeable cap dielectric 86 is depositedusing chemical vapor deposition (CVD), spin on deposition, or acombination thereof.

FIGS. 13 and 14 depict forming a contact 91, 95 to a metal line 10 ofthe plurality of metal lines, wherein at least one of the permeable capdielectric 86 and the sacrificial filler material 85 obstruct thecontact from filling said at least one air gap 20.

FIG. 13 depicts forming an interlevel dielectric layer 87 over thepermeable cap dielectric 86, patterning the interlevel dielectric layer87 with an etch that is selective to at least one of the permeable capdielectric 86 and the sacrificial filler material 85 to form a trench90; and forming a trench liner material 91.

The interlevel dielectric layer 87 may be selected from the groupconsisting of silicon containing materials such as SiO₂, Si₃N₄,SiO_(x)N_(y), SiC, SiCO, SiCOH, and SiCH compounds, the above-mentionedsilicon containing materials with some or all of the Si replaced by Ge,carbon doped oxides, inorganic oxides, inorganic polymers, hybridpolymers, organic polymers such as polyamides or SiLK™, other carboncontaining materials, organo-inorganic materials such as spin-on glassesand silsesquioxane-based materials, and diamond-like carbon (DLC), alsoknown as amorphous hydrogenated carbon, α-C:H). Additional choices forthe interlevel dielectric layer 87 include any of the aforementionedmaterials in porous form, or in a form that changes during processing toor from being porous and/or permeable to being non-porous and/ornon-permeable.

Patterning the interlevel dielectric layer 87 with an etch that isselective to at least one of the permeable cap dielectric 86 and thesacrificial filler material 85 to form a trench 90 may employphotolithography and etch processes similar to those described above inthe embodiments described with reference to FIGS. 1-10. In someembodiments, patterning of the interlevel dielectric layer etchesthrough said permeable cap dielectric, but does not impact the integrityof the sacrificial filler material 85.

FIG. 14 depicts filling the trench 90 with an electrically conductivematerial to form a contact 91, 95 to a metal line of the plurality ofmetal lines, and removing said sacrificial filler material 85. Thecontact may include a trench liner 91 and an electrically conductivematerial fill 95.

The trench liner 91 may be a seed layer, diffusion barrier or adhesionlayer that can be deposited using at least one of atomic layerdeposition (ALD), chemical vapor deposition (CVD), plasma vapordeposition (PVD), pulsed nucleation layer (PNL), pulsed deposition layer(PDL), plasma-enhanced ALD and plasma-enhanced CVD. The trench liner 91may be composed of a metal, such as copper, aluminum, tungsten,tantalum, titanium and combinations thereof.

The electrically conductive fill material 95 may be formed usingdeposition methods, such as CVD or PVD. Examples of PVD methods suitablefor forming the electrically conductive fill material 95 includesputtering, plating, electroplating, electroless plating, andcombinations thereof. The electrically conductive fill material 95 mayinclude, but is not limited to: tungsten, copper, aluminum, silver, goldand alloys thereof. Following deposition, the upper surface of theelectrically conductive fill material may be planarized, e.g.,planarized by chemical mechanical planarization (CMP). A secondinterlevel dielectric layer 96 may be formed atop the planarized uppersurface of the electrically conductive fill material

FIG. 14 depicts removing the sacrificial filler material 85 from the airgaps 20. The sacrificial filler material 85 may be thermally decomposedinto a gas, wherein the gas out diffuses from the air gap through thepermeable cap dielectric 86. Thermal decomposition of the sacrificialfiller material 85 may include annealing the structure depicted in FIG.14 in a furnace having controlled, inert or vacuum atmosphere. Theincrease in temperature is slowly ramped to about 350° C. to 450° C. fora time sufficient to complete removal of the sacrificial filler material85 and its decomposition by-products. The end point may be monitoredusing a mass spectrometer. The thermal decomposition method may continueuntil an entirety of the sacrificial filler material 85 has decomposed,leaving air dielectric, i.e., gaseous air, i.e., no solid material, inits place. The decomposition byproducts are gasified and diffuse throughpermeable hard permeable cap dielectric 86 and are removed by vacuum.

FIG. 15 is a top down view depicting an interconnect structure to metallines 10 separated by air gaps 20 that does not include an exclusionzone. An exclusion zone is an area in which a dielectric material ispresent between lines, i.e., completely filling the area betweenadjacent lines, in which the vias are formed to avoid the vias fromentering an air gap. As depicted in FIG. 15, the entirety of the spaceseparating adjacent metal lines are provided air gaps 20. FIG. 15depicts an electrical device that includes a plurality of metal lines 10in a region of a substrate positioned in an array of metal lines allhaving parallel lengths. FIG. 15 depicts a plurality of air gaps 20between the metal lines 10 in a same level as the metal lines, whereinan air gap 20 is present between each set of adjacent metal lines. FIG.15 further depicts a plurality of interconnects 74, 95 in electricalcommunication with said plurality of metal lines 10, wherein anexclusion zone for the plurality of interconnects 74, 95 is not presentin said array of metal lines 10.

The cross section depicted by section line A-A illustrates theembodiment described above with reference to FIGS. 11-14. In thisembodiment, the plurality of interconnects 95 in electricalcommunication with said plurality of metal lines 19 includesinterconnects that are present extending over an air gap 20, but doesnot extend into the air gap 20, as depicted in FIG. 14. In thisembodiment, the bottom surface of the interconnect 91, 95 provides aportion of an upper surface of the air gap 20. In some embodiments, apermeable dielectric cap 86 is adjacent to the bottom surface of theinterconnect 91, 95 and provides an abutting upper surface of the airgap adjacent 20 to the upper surface of the air gap 20 provided by theinterconnect. The cross section depicted by section line B-B illustratesthe embodiment described above with reference to FIGS. 1-10. In thisembodiment, the plurality of interconnects 73, 74 are self-aligned tothe plurality of metal lines 10.

Having described preferred embodiments of systems, apparatuses anddevices including an electrical fuse (which are intended to beillustrative and not limiting), it is noted that modifications andvariations can be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments disclosed which are within the scopeof the invention as outlined by the appended claims. Having thusdescribed aspects of the invention, with the details and particularityrequired by the patent laws, what is claimed and desired protected byLetters Patent is set forth in the appended claims.

What is claimed is:
 1. A method of forming an interconnect to anelectrical device comprising: forming at least one air gap betweenadjacent metal lines in a plurality of metal lines by forming aconformal dielectric layer on sidewalls and upper surfaces of saidplurality of metal lines and forming a low-k air gap forming dielectricthat is non-conformally deposited and encloses said at least one air gapwithin a space between said adjacent metal lines by pinching off anopening to said space to provide an upper surface of the at least oneair gap that is substantially coplanar with the upper surface of theadjacent metal lines, the step coverage of a deposition process forforming the low-k air gap forming dielectric is selected for providingan undulating upper surface for the low-k air gap forming dielectrichaving peaks aligned to the plurality of metal lines and low points inthe undulating upper surface for the low-k air gap forming dielectricaligned to the at least one air gap; depositing a conformal bilayer hardmask directly atop the undulating upper surface for the low-k air gapforming dielectric, wherein the conformal bilayer hardmask includes afirst hard mask dielectric layer of silicon nitride in direct contactwith the undulating upper surface for the low-k air gap formingdielectric and a second hard mask dielectric layer of a metal nitride indirect contact with the first hard mask dielectric layer; removing aportion of the second hard mask dielectric layer to expose a portion ofthe first hard mask dielectric layer that is overlying a peak of thelow-k air gap forming dielectric having peaks aligned to the pluralityof metal lines; removing a portion of the first hard mask layer that isoverlying the peak of the low-k air gap forming dielectric having peaksaligned to the plurality of metal lines, while a remaining portion ofthe first hard mask layer that is not present on the peak is protectedby masking; forming a trench through the low-k air gap formingdielectric using a remaining portion of the first hard mask layer ofsilicon nitride as an etch mask to expose the metal line without openingsaid at least one air gap; and forming a contact to the metal line insaid trench.
 2. The method of claim 1, wherein forming the plurality ofmetal lines comprises: forming a plurality of line trenches in a low-kline dielectric layer; forming a liner material in the line trenches;and forming said plurality of metal lines on the liner material in theplurality of line trenches.
 3. The method of claim 2, further comprisingselectively forming a metal cap layer on an upper surface of theplurality of metal lines.
 4. The method of claim 3, wherein said formingsaid air gap further comprises: removing a damaged portion of the low-kline dielectric layer to open a space between said adjacent metal linesin said plurality of metal lines; forming said conformal dielectriclayer on sidewalls and upper surfaces of said plurality of metal lines;and forming said low-k air gap forming dielectric, wherein said low-kair gap forming dielectric is non-conformally deposited and enclosessaid air gap within said space between said adjacent metal lines bypinching off an opening to said space.
 5. The method of claim 4comprising: forming a first etch mask over the conformal bilayer hardmask, wherein an opening in the first etch mask is overlying at leastone of said metal lines and at least one of said air gap; removing anexposed portion of the second hardmask layer in said opening selectivelyto the first hardmask layer; and removing the first etch mask.
 6. Themethod of claim 5, wherein removing the portion of the first hard masklayer that is overlying the peak of the low-k air gap forming dielectrichaving peaks aligned to the plurality of metal lines, while theremaining portion of the first hard mask layer that is not present onthe peak is protected by masking comprises: forming a sacrificialdielectric layer atop the conformal bilayer hard mask; forming a secondetch mask over the sacrificial dielectric layer; forming said opening inthe sacrificial dielectric layer with a selective etch to the portion ofthe first hard mask layer that is overlying the peak of the low-k airgap forming dielectric having peaks aligned to the plurality of metallines; and removing the portion of the first hard mask layer that isoverlying the peak of the low-k air gap forming dielectric having peaksaligned to the plurality of metal lines with an etch that is selectiveto the sacrificial dielectric layer and the low-k air gap formingdielectric.
 7. The method of claim 6, wherein said forming the trenchthrough the low-k air gap forming dielectric using the remaining portionof the first hard mask layer as an etch mask to expose a metal linewithout opening said at least one air gap comprises: an anisotropic etchthat is selective to the metal cap layer that is present atop the metallines; and removing the second etch mask.
 8. The method of claim 7,wherein forming the contact to the metal line in the trench comprises:removing the remaining portion of the first hard mask layer; removingthe sacrificial dielectric layer; and forming an electrically conductivematerial in the trench in contact with the metal line.